hey i have one of those. they are not very hard to make at all. john has a very good how to on his site.
i cheated when i made mine, i mostly used 6-32 all thread. that made it so much easier to adjust and set how long the arms for the 8 switches. i used 1/4 key-stock to connect the arms to the king pin. that gives you adjustment to get everything to fit your hand just right.
this would be grate in a car if you wanted to mount a keyboard on to the steering wheel its self. just think your hand would never have to move off the wheel when go to the keys.